Diversity of TCRAV and TCRBV sequences used by human T-cell clones specific for a minimal epitope of Bet v 1, the major birch pollen allergen

Interaction of allergens, major histocompatibility complex molecules, and T cell receptors: a 'ménage à trois' that opens new avenues for therapeutic intervention in type I allergy

T cells are major players in the initiation and perpetuation of the allergic immune response. In this review, we summarize the current knowledge on allergen recognition by T lymphocytes and address the components of the trimeric recognition complex: T cell receptors, major histocompatibility complex molecules, and allergen-derived peptides. Furthermore, possible implications of this scientific background for future therapeutic developments are discussed.

Naturally processed T cell-activating peptides of the major birch pollen allergen

BACKGROUND

Although antigen processing and presentation of allergens to CD4(+)T lymphocytes are key events in the pathophysiology of allergic disorders, they still remain poorly understood.

OBJECTIVE

To investigate allergen processing and presentation by dendritic cells using the major birch pollen allergen Bet v 1 as a model.

METHODS

Endolysosomal extracts of dendritic cells derived from patients with birch pollen allergy were used to digest Bet v 1. Dendritic cells were pulsed with Bet v 1, and peptides were eluted from MHC class II molecules. Peptides obtained by either approach were sequenced by tandem mass spectrometry. Bet v 1-specific T-cell cultures were stimulated with HLA-DR-eluted Bet v 1-derived peptides. Bet v 1-specific T-cell lines were generated from each patient and analyzed for epitope recognition.

RESULTS

A high proportion of Bet v 1 remained intact for a long period of endolysosomal degradation. The peptides that appeared early in the degradation process contained frequently recognized T-cell epitopes. Bet v 1-derived peptides eluted from MHC class II molecules corresponded to those generated by endolysosomal degradation, matched known T-cell epitopes, and showed T cell-activating capacity. The Bet v 1-specific T-cell line of each individual harbored T cells reactive with peptides located within the MHC class II-eluted Bet v 1-derived sequences demonstrating their occurrence in vivo.

CONCLUSION

We report for the first time how epitopes of allergens are generated and selected for presentation to T lymphocytes. The limited susceptibility of Bet v 1 to endolysosomal processing might contribute to its high allergenic potential.

Functional Analysis of Birch Pollen Allergen Bet v 1-Specific Regulatory T Cells

Allergen-specific immunotherapy using peptides is an efficient treatment for allergic diseases. Recent studies suggest that the induction of CD4+ regulatory T (Treg) cells might be associated with the suppression of allergic responses in patients after allergen-specific immunotherapy. Our aim was to identify MHC class II promiscuous T cell epitopes for the birch pollen allergen Bet v 1 capable of stimulating Treg cells with the purpose of inhibiting allergic responses. Ag-reactive CD4+ T cell clones were generated from patients with birch pollen allergy and healthy volunteers by in vitro vaccination of PBMC using Bet v 1 synthetic peptides. Several CD4+ T cell clones were induced by using 2 synthetic peptides (Bet v 1(141-156) and Bet v 1(51-68)). Peptide-reactive CD4+ T cells recognized recombinant Bet v 1 protein, indicating that these peptides are produced by the MHC class II Ag processing pathway. Peptide Bet v 1(141-156) appears to be a highly MHC promiscuous epitope since T cell responses restricted by numerous MHC class II molecules (DR4, DR9, DR11, DR15, and DR53) were observed. Two of these clones functioned as typical Treg cells (expressed CD25, GITR, and Foxp3 and suppressed the proliferation and IL-2 secretion of other CD4+ T cells). Notably, the suppressive activity of these Treg cells required cell-cell contact and was not mediated through soluble IL-10 or TGF-beta. The identified promiscuous MHC class II epitope capable of inducing suppressive Treg responses may have important implication for the development of peptide-based Ag-specific immunotherapy to birch pollen allergy.

Identification of new MHC-restriction elements for presentation of the p210(BCR-ABL) fusion region to human cytotoxic T lymphocytes

Chronic myelogenous leukemia (CML) is characterized by a t(9;22) translocation resulting in expression of BCR-ABL fusion oncoproteins which are unique to the leukemic cells, necessary for oncogenesis, and potentially immunogenic. We have previously shown that human dendritic cells transduced with an adeno-associated virus vector encoding the fusion region of the b3a2 splice variant (p210(b3a2)) of the BCR-ABL oncoprotein elicit specific T-cell responses in vitro. Two cytotoxic T lymphocyte (CTL) clones generated in this fashion displayed restriction with previously unreported HLA alleles. The first, T1/B9, was CD4(+) and restricted by DRB5*0101 (autologous) or DRB1*1101 (allogeneic). The minimum cytotoxic epitope (MCE) binding to DRB5*0101 for this clone was identified as FKQSSKALQ, overlapping the p210(b3a2) fusion point (boldface). The MCE of DRB1*1101 for this clone differed from DRB5*0101, but also included the fusion point. The clonality of CTL T1/B9 was verified by analyses of TCRalpha/beta chain usage and DNA sequence analyses. To our knowledge, this is the first description of a single clone recognizing both DRB5*0101 and DRB1*1101. The other CTL clone, T1/33, was CD8+ and recognized HLA-B*3501 or B*3503 complexed with an MCE, RPVASDFEP, derived from the c-abl sequence in proximity to the p210(b3a2) fusion point. K562 cells transfected with plasmids encoding HLA-DRA + B5*0101, B*3501, or B*3503 but not controls expressing DRA + DRB1*1501 were lysed by cognate CTL clones, confirming that DRB5*0101 and B*3501/3 could present p210(b3a2) joining region epitopes via endogenous processing. The identification of three additional HLA alleles (DRB5*0101, B*3501, and B*3503) presenting the p210(b3a2) fusion-region antigen will broaden the application of vaccine strategies for targeting CML cells. The findings of single CTL clones cross-recognizing autologous (DRB5*0101 or B*3501) and allogeneic (DRB1*1101 or B*3503) HLA alleles presenting BCR-ABL fusion-region epitopes implies the potential separation of graft-versus-leukemia from graft-versus-host effects.

Identification of isoform-specific T-cell epitopes in the major timothy grass pollen allergen, Phl p 5

BACKGROUND

The involvement of CD4+ T cells in the pathophysiology of atopic disease is well established.

OBJECTIVE

To gain further insight into the activation requirements for allergen-specific T cells, we characterized epitope specificity, HLA restriction and T-cell receptor (TCR) usage for T cells specific to Phl p 5, the group 5 major allergen of the grass Phleum pratense.

METHODS

To identify the T-cell epitopes of Phl p 5, three Phl p 5-specific T-cell lines (TCLs) and 15 T-cell clones (TCCs) generated from the peripheral blood of three grass-allergic patients were tested with recombinant truncated Phl p 5a fragments and synthetic Phl p 5b peptides representing these two different recombinant Phl p 5 isoallergens. Additional activation experiments with HLA-subtyped antigen-presenting cells and flow cytometry analysis with TCR V-specific mAb were performed to further characterize the activation requirements for Phl p 5-specific TCCs.

RESULTS

At least nine distinct T-cell specificities were identified and the T-cell epitopes recognized differed considerably among the three patients. Most of the epitopes found were isoform-specific, whereas three epitopes were shared between Phl p 5a and 5b. Several human leucocyte antigen (HLA) class II molecules were involved in the recognition of Phl p 5. Different HLA restriction specificities were even found among TCCs specific to the same epitope region. All TCCs were TCR-alpha/beta positive, and an overrepresentation of TCR Vbeta 3.1+ clones among TCCs specific to Phl p 5 appear to exists as 31% (4/13) of the TCCs expressed TCR Vbeta 3.1 (compared with 5% TCR Vbeta 3.1+ T cells in human peripheral blood) with no correlation with epitope specificity or HLA restriction.

CONCLUSION

The T-cell reactivity of the three grass-allergic patients investigated shows that isoallergen-specific T-cell epitopes are found throughout the peptide backbone of Phl p 5a and Phl p 5b, and dominant T-cell epitopes of Phl p 5 were not identified. This indicates that a mixture of at least full-length rPhl p 5a and rPhl p 5b may be required to target the total Phl p 5-specific T-cell response of atopic patients.

The role of allergen-specific T cells in the allergic immune response: relevance to allergy vaccination

Recent research has elucidated many of the immunologic mechanisms that underlie atopic allergies. In particular, it has become clear that the role of CD4+ allergen-specific T cells is crucial for the induction of IgE and eosinophilia, factors that mediate the immediate hypersensitivity reaction and late-phase responses, respectively. Therefore, the reactivity patterns and activation requirements of allergen-specific T cells are important parameters for understanding and manipulating the allergic immune response. This review addresses these issues and discusses their relevance to the further development of allergy vaccines.

Identification of a highly promiscuous and an HLA allele-specific T-cell epitope in the birch major allergen Bet v 1: HLA restriction, epitope mapping and TCR sequence comparisons

BACKGROUND

Allergen-specific CD4+ T cells play an important regulatory role in atopic allergy.

OBJECTIVE

To investigate the human leucocyte antigen (HLA) restriction and T-cell receptor (TCR) usage of allergen-specific T-cell clones (TCCs) that react with defined epitopes of Bet v 1, the major birch pollen allergen.

METHODS

Five Bet v 1-specific TCCs derived from two birch pollen-allergic individuals and specific for Bet v 1, were epitope-mapped with overlapping synthetic peptides. In addition, HLA-restriction and TCR CDR3 sequences were determined.

RESULTS

Three TCCs reacted with a Bet v 1 peptide containing amino acid residues 21-33 (BP21), the other two TCCs reacted with a minimal peptide comprising residues 37-45 (BP37). Studies using neutralizing anti-HLA-monoclonal antibodies and HLA-typed APCs showed that the BP37-specific TCCs were restricted by a HLA-DQA1*0301/DQB1*0603 heterodimer. In contrast, BP21 was recognized in a highly promiscuous manner. TCCs recognizing this sequence were restricted by HLA-DPB1*0201, a HLA-DQA1*0201/DQB1*0201 heterodimer, or HLA-DRB3*0101. Reverse transcription-polymerase chain reaction with primers for all known TCRAV and TCRBV gene segments, followed by CDR3 region sequencing, revealed the usage of five different TCRAV and four different TCRBV gene segments by the TCCs, as well as diversity in the joining region. All BP21-specific TCCs contained a negatively charged residue in their CDR3alpha regions, the CDR3beta regions showed a high concentration of polar and OH-group bearing residues. BP37-specific TCCs shared the amino acid combination LY in the middle of their CDR3alpha regions, the CDR3beta regions showed high concentration of OH-group bearing or charged residues.

CONCLUSIONS

This study shows the existence of a highly promiscuous T-cell epitope in Bet v 1. The presence of additional T-cell epitopes in Bet v 1 may, however, hamper the clinical applicability of the epitope. Likewise, the diversity in TCR usage by T cells recognizing the epitope does not support the development of TCR-directed immunotherapy for birch pollen allergy.

Long-Lived Th2 Clones Specific for Seasonal and Perennial Allergens Can Be Detected in Blood and Skin by Their TCR-Hypervariable Regions

We investigated the longevity of allergen-specific Th cells derived from patients suffering from either allergic rhinitis or atopic dermatitis. T cell clones (TCC) specific for seasonal and perennial allergens were raised. To determine whether these TCC were long-lived in vivo, PBMC and allergen-specific polyclonal T cell lines, collected and established inside a period of up to 4 years, were screened for the TCC of interest. For this purpose, a T cell tracing protocol was established in which oligonucleotides specific for the TCR β-chain hypervariable junctional region were used as tools to identify each particular TCC. Seven pollen-specific TCC and two house dust mite-specific TCC, with a Th2-like cytokine production pattern in vitro, were demonstrated to be long-lived memory T cells in vivo. Specificity of the tracing protocol was ascertained by TCR sequence analysis. We conclude that allergen-specific TCC can persist for years, evidence for which can be monitored in blood, but also in the target organ of the allergic disorder. The data indicate that in vitro-characterized, allergen-specific, long-lived TCC may well reflect a repertoire of T lymphocytes of pathogenetic importance in vivo.

Epitope analysis of birch pollen allergen in Japanese subjects

Birch pollen is a very common cause of nasal allergy (pollinosis) not only in Scandinavia, Europe, Canada, and the northern part of the United States but also in Hokkaido, Japan. We have previously reported a positive association between the HLA-DR9 phenotype and the development of birch pollen allergy in Japanese subjects. However, there is little information about T cell epitopes of birch pollen which are presented by HLA class II molecules other than HLA-DR9. Therefore, we analyzed the difference in T cell epitope usage in patients who had HLA-DR9 versus those who did not. Seven Japanese patients with birch pollinosis were studied. Some groups of peptides representing T cell epitopes (Betula verrucosa; Bet VI peptides, p7-33, p23-46, p138-160) appeared to be shared by the majority, while another peptide (Bet VI p72-95) was recognized predominantly by patients who expressed HLA-DR9 and/or HLA-DQ3 molecules. Moreover, seven T cell clones and eight T cell lines were generated from two patients who did not have HLA-DR9 or HLA-DQ3. Using some of these T cell clones/lines, we investigated the relationship between HLA class II molecules and antigenic peptides. One of these T cell clones recognized antigenic peptides in the context of the HLA-DQ1 molecule. To our knowledge, this is the first indication that the epitope on Bet VI can be presented by the HLA-DQ molecule.

Sequence comparisons of the CDR3 hyper-variable loops of human T cell receptors specific for three major T cell epitopes of the birch pollen allergen Bet v 1

We have analysed the T cell receptor (TCR) alpha and beta chain sequences of 16 human CD4+ T cell clones (TCCs) specific for three important epitopes of the major birch pollen allergen Bet v 1. The TCCs were raised from the peripheral blood of eight patients with birch pollen allergy, showing allergic rhino-conjunctivitis and allergic asthma. The TCCs from these individuals were specific for Bet v 1-derived peptides: amino acids (aa)77-92 (epitope 1), aa93-108 (epitope 2) and aa113-126 (epitope 3). The DNA sequence analysis of the TCRAV and BV regions revealed heterogeneous repertoires for recognition of the peptides. Multiple combinations of AV/AJ and BV/BJ were used. However, some inter-individual restriction was evident. A limited selection of AVS and the normally infrequently used BV1S4 was obvious in TCCs specific for epitope 1. The TCRBV13 was more frequent in TCCs recognizing epitope 3. A very narrow distribution in length could be seen in the CDR3 sequences of the beta chain of TCRs with specificity for epitopes 1 and 2. Inter-individual positional micro-restriction was observed for the aa motif LR in the tCDR3 (epitope 1), for the aa residue M in the alphaCDR3 and for the aa residue G in the betaCDR3 (epitope 3). Our results illustrate clearly that each antigenic peptide derived from a single allergen, is capable of selecting different characteristics in the responding repertoire of TCRs, thus increasing the complexity of allergen-recognition by T lymphocytes. Therefore, our findings limit the potential use of TCR targeted therapeutical strategies in Type I allergy.

Comparative sequence analysis of the human T cell receptor TCRA and TCRB CDR3 regions

There is increasing experimental and structural support for the idea that the T cell receptor CDR3 region makes primary contact with the peptide held in the MHC groove. As part of the efforts to understand this critical region of the TCR more fully, we have cloned and sequenced several hundred human TCR transcripts and made an analysis of the amino acids found in the CDR3 region. The length of the CDR3 region is found to be relatively conserved and similar in both TCRA and TCRB sequences. In contrast, the amino acid contribution from individual gene segments varies between the TCRA and TCRB transcripts with the longer TCRAJ segment largely making up for the lack of the D segment in the TCRA gene. Amino acid usage in the CDR3 region is nonrandom with a predominance of charged or polar residues in the TCRA transcript and a majority of glycines in TCRB. Analysis of CDR3 sequence in TCR transcripts cloned from antigen-specific cytotoxic T cells reveals differences in the pattern of amino acid conservation for both chains. The TCRA CDR3 region shows less length conservation than TCRB, but selection for particular TCRAJ segments is marked. In contrast, TCRBV segments are highly conserved and are associated with an amino acid motif in the N region. These findings reveal the different mechanisms that are used by the TCRA and TCRB genes to generate diversity in the CDR3 region and raise the possibility that the two chains may play nonequivalent roles in antigen selection.